It'll be fine to start the cycle but you might want a little more so that you can stack it better. It really depends on how you aquascape it. But, IMO, 45 lbs probably won't be enough to do the tank.
About the damsel thing, some people on here will say it's cruel, others will say go for it. I started my tank with damsels and I still have them. They survived and are tougher now. I do regret putting them in though, not because of animal "rights" but b/c they're a pain to get out later when you have a bunch of LR in there.